The early-Christian writer Tertullian is commonly associated with the statement ‘credo quia absurdum’ – I believe because it is absurd. However, this sentence (first ascribed to him in the early-modern period) cannot be found in Tertullian’s work. As this article seeks to demonstrate, the very idea behind it is neither in line with his conception of the relationship between faith and reason. The same Tertullian who decries the Greek philosophy of ‘Athens’ builds on Stoic views to reinforce and clarify his theological positions. Rather than as a total rejection of ancient philosophy, his preference for ‘Jerusalem’ should therefore be read as a critique of the way in which some Greek philosophers philosophized and the unchristian conclusions that they reached. Tertullian did not shun philosophical argumentation as such. As a matter of fact, his argument based on absurdity resembles one the rhetorical tropes described in Aristotle’s Rhetoric. The real conflict in Tertullian is that between the divine wisdom from heaven and the worldly wisdom of the heretics.